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23 March 2005 High NA-fibers: silica-based fibers for new applications
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For medical and analytical applications, thick-core fibers based on synthetic silica are widely spread. In many cases, the fibers are used as a light-guiding medium only; therefore, the coupling efficiency between the light-emitting area and the accepting fiber is of great importance described easily by the light acceptance cone related to the numerical aperture of the fiber. In the past, all-silica fibers with un-doped silica core and fluorine-doped silica cladding have been used for different applications. However, these fibers are restricted in respect to a low numerical aperture of typically 0.22. To increase the numerical aperture, different polymers can be used for cladding material. In addition to standard polymers, Teflon-AF is an attractive candidate for significantly higher NAs of approx. 0.65. In parallel, a new class of all-silica fibers was developed with high NA, the so-called “Air-clad” or microstructured fibers. Longitudinal microstructured holes, in the order of the wavelength, form the cladding-region together with the surrounding silica. The dimensions of the microstructure dictate the critical angle for light transmission in the core, rather than the refractive index of the cladding material. The light guiding properties of different fibers will be compared. Especially the optical transmission from the UV-region up to the NIR-region will be discussed. Due to the wavelength-dependent mean value of the refractive index (RI) in the cladding, the definition of numerical aperture has to be adjusted. Especially, the UV-damage within Teflon-coated fibers and the microstructured fibers will be described in detail.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Karl-Friedrich Klein, Hanns Simon Eckhardt, Christiane Vincze, Stephan Grimm, Johannes Kirchhof, Jens Kobelke, Jim Clarkin, and Gary Nelson "High NA-fibers: silica-based fibers for new applications", Proc. SPIE 5691, Optical Fibers and Sensors for Medical Applications V, (23 March 2005);


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